As estruturas com maior possibilidade de fossilização do esqueleto dos Chondrichthyes são aquelas mais mineralizadas, tais como dentes, escamas, espinhos cefálicos e de nadadeiras. Na Formação Rio do Rasto, os Chondrichthyes estão representados predominantemente por dentes e espinhos de nadadeiras. Na presente dissertação, foram estudados espécimes coletados em um afloramento do Membro Serrinha da Formação Rio do Rasto próximo ao quilômetro 20 da BR-153 no Município de Jacarezinho, Estado do Paraná, Brasil. O material corresponde a dois conjuntos, um representado por dois espinhos de nadadeira e o outro por vários dentes, todos depositados no Museu de Ciências Naturais do Setor de Ciências Biológicas da Universidade Federal do Paraná. No primeiro conjunto as características apresentadas pelos espinhos permitiram atribuí-los a uma nova espécie de Sphenacanthidae, enquanto que as características do segundo conjunto permitiram atribuir os dentes a uma nova espécie de Xenacanthidae. A associação fóssil na localidade-tipo e no mesmo horizonte estratigráfico da Formação Rio do Rasto indica que estas ocorrências de tubarões podem representar mais um registro de água doce para os xenacantídeos e esfenacantídeos. / The chondrichthian skeletal structures with greater potential of fossilization are the most mineralized such as teeth, scales, fin spines and cephalic spines. In the Rio do Rasto Formation the Chondrichthyes are represented by fin spines and teeth. The studied material came from an outcrop of Serrinha Member of the Rio do Rasto Formation, close to km 20, by the road BR-153 in the city of Jacarezinho, State of Paraná, Brazil. The studied material are two sets, one represented by two fin spines and the other by several teeth, all housed in the “Museu de Ciências Naturais do Setor de Ciências Biológicas da Universidade Federal do Paraná” - UFPR Natural Sciences Museum. In the first set, the features shown allow to ascribe the finspines to a new species of Sphenacanthidae, while the features of the second set allow to ascribe the teeth a new species of Xenacanthidae. The fossil association in the type locality and in the same stratigraphical horizon in the Rio do Rasto Formation indicates that these shark occurrences could represent another freshwater record for the xenacanthids and sphenacanthids.

Sharks are particularly vulnerable to over-exploitation. Although catsharks are an important component of the near-shore marine biodiversity in South Africa and most of the species are endemic, little is known about their movement patterns, home range and population size. With an increasing number of recreational fishers this information is crucial for their conservation. The aims of this study were threefold. Firstly, to identify and analyze existing data sources on movement patterns and population dynamics for four catshark species: pyjama (Poroderma africanum), leopard (P. pantherinum), puffadder (Haploblepharus edwarsii) and brown (H. fuscus). This highlighted a number of shortcomings with existing data sets, largely because these studies had diverse objectives and were not aimed solely at catsharks. Secondly, a dedicated study was carried out for a limited area, testing a number of methods for data collection, and where appropriate the data was analyzed to determine movement patterns and population numbers. Thirdly, the most appropriate methodology for future studies (with similar objectives) was identified, and the results of the study were used to propose a number of conservation measures. All species of catsharks exhibited strong site fidelity and limited dispersal for extended periods. A few individuals did, however, travel distances in excess of 150 km. Significant trends in temporal abundance were not observed, nevertheless, there was some evidence for higher catches from September to December. Population estimates for the study area were low, with P. africanum having the smallest population size while H. fuscus had the highest population size within the restricted study area. Limited movements, high site fidelity and small population sizes emphasize their vulnerability and suggest that catsharks would benefit from no-take marine protected areas.

No description available.

No description available.

En este trabajo se analizan la morfología del aparato reproductor, la biología reproductiva y la distribución y abundancia de la raya Atlantoraja cyclophora en el Distrito Biogeográfico Bonaerense, entre los 34° y 42°S. El material analizado provino de campañas de investigación realizadas por el Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP) y de la compra de ejemplares desembarcados en el Puerto de Mar del Plata. La organización anatómica del sistema reproductor de A. cyclophora es semejante a la observada en otros Rájidos. Tanto machos como hembras, presentan gónadas pares e igualmente funcionales asociadas con el órgano epigonal. Los conductos genitales de los machos están revestidos por un epitelio simple cilíndrico ciliado, que se pliega tomando el aspecto de pseudoestratificado hacia la porción más distal. Los espermatozoides se encuentran libres en el inicio de los conductos y se agregan progresivamente resultando en un empaquetamiento similar al de tipo espermatozeugmata en la vesícula seminal. Los conductos genitales de las hembras están adaptados a la oviparidad. El grado de desarrollo y complejidad de las glándulas oviductales se refleja en la producción de cápsulas coriáceas rígidas y resistentes para la protección del embrión en desarrollo. Las adaptaciones morfológicas e histológicas de los úteros contribuirían con oscurecimiento, esclerotización y desplazamiento de las cápsulas para oviposición. A partir del análisis de los parámetros reproductivos se detectó dimorfismo sexual en la longitud total máxima (LT), ancho de disco (AD), peso total (PT) y peso del hígado (PH) con respecto a la longitud. Las hembras resultaron ser más largas, anchas y pesadas que los machos para una misma longitud. El carácter dimórfico de las relaciones PT-LT y PH-LT estaría asociado al inicio de la madurez sexual y a los requerimientos energéticos que implica la reproducción. La longitud a la cual el 50% de los individuos maduran sexualmente (LT50) se estimó en 537 mm LT para machos y 570 mm LT para hembras y corresponde al 79,7% y 80,4% de la talla máxima observada (674 mm LT machos y 709 mm LT hembras), respectivamente. Estos resultados son consistentes con lo observado en la mayoría de los Rájidos e implican que los individuos de A. cyclophora presentan una etapa juvenil extendida y al llegar a la madurez sexual la mayor inversión energética sería destinada a la reproducción. Asimismo, los valores de LT50 registrados aquí, superan a los estimados para esta especie en el Distrito Sudbrasileño y apoyan la tendencia del incremento de los parámetros de historia de vida en función de la latitud. Con respecto a la actividad reproductiva, las hembras de A. cyclophora presentan un ciclo reproductivo anual con un posible pico estacional durante la primavera mientras que los machos tendrían la capacidad de reproducirse a lo largo del año, dada la falta de variación en el peso testicular. Dentro del área de estudio la población de A. cyclophora se compone principalmente por individuos juveniles. La especie presenta un patrón de distribución espacial heterogéneo, concentrándose principalmente en la zona de El Rincón y frente a la costa este y sur de Uruguay, donde se registraron las mayores abundancias. Atlantoraja cyclophora fue capturada entre los 10,9 y 53,6 m de profundidad, a temperaturas entre 8,5 y 19,2°C y entre los 26,6 y 34,1 ppm de salinidad. Tanto para el área del Río de la Plata como en El Rincón, la especie presenta preferencia por la profundidad y no sería afectada significativamente por las variaciones estacionales de temperatura de fondo. Los juveniles se distribuyen desde aguas de baja profundidad (13 m) hasta la isobata de los 50 m, mientras que los adultos predominan a partir de los 30 m de profundidad La región costera bonaerense es un área que alberga una gran variedad de especies marinas y cumple un rol importante en los ciclos de vida de los peces cartilaginosos. A su vez, esta región concentra los principales puertos de desembarque de tiburones y rayas, siendo estas últimas declaradas bajo una misma categoría sin discriminar a nivel específico. Atlantoraja cyclophora es capturada como fauna acompañante de otras pesquerías industriales y se encuentra entre las principales especies de rayas desembarcadas. Las zonas de mayor concentración de la especie se componen principalmente de estadios ontogenéticos de los que depende la tasa de crecimiento de la población (juveniles y hembras con cápsulas). Este hecho, sumado a la prolongada etapa juvenil que presentan los individuos, resalta su vulnerabilidad frente a la explotación pesquera. Los resultados de trabajo aportan información significativa sobre la ecología reproductiva de A. cyclophora que, además de su interés biológico, pueden ser de utilidad para la elaboración de medidas de manejo y conservación de la especie. / The morphology of the reproductive system, the reproductive biology and the distribution and abundance of the skate Atlantoraja cyclophora in the Biogeographic Bonaerensean District, between 34° and 42°S, are analyzed in this work. The material came from research cruises carried out by the National Institute of Fisheries Research and Development (INIDEP) and from the purchase of specimens landed in the Mar del Plata Port. The anatomical organization of the reproductive system of A. cyclophora is similar to that observed in other Rajids. Both, males and females, present pairs gonads, equally functional, and associated with the epigonal organ. Male’s genital ducts are lined by a simple ciliated columnar epithelium, which folds taking the aspect of pseudostratified towards the most distal portion. The sperm are free at the beginning of the ducts and are added progressively resulting in a similar aggregation to the spermatozeugmata type in the seminal vesicle. Female’s genital ducts are adapted to oviparity. The degree of development and complexity of the oviductal glands is reflected in the production of rigid and resistant egg capsules for the protection of the developing embryo. The morphological and histological adaptations of the uteri would contribute with tanning, sclerotization and displacement of the capsules for oviposition. From the analysis of the reproductive parameters, sexual dimorphism was detected in the maximum total length (TL), disc width (DW), total weight (TW) and liver weight (LW) with respect to the length. Females were longer, wider and heavier than males for the same length. The dimorphic character of the TW-TL and LW-TL relationships would be associated with the onset of sexual maturity and with the energetic requirements that reproduction implies. The length at witch the 50% of the individuals attain the sexual maturity (TL50) was estimated at 537 mm TL for males and 570 mm TL for females and corresponds to 79,7% and 80,4% of the maximum size observed (674 mm TL males and 709 mm TL females), respectively. These results are consistent with those observed in most of the Rajids and imply that the individuals of A. cyclophora have an extended juvenile stage, and when they reach sexual maturity, the greatest energy investment would be destined to reproduction. Likewise, the values of TL50 recorded here overcome those estimated for this species in the Southbrazilian District, and support the tendency of the increase of the life history parameters related to latitude. With respect to the reproductive activity, A. cyclophora females present an annual reproductive cycle with a possible seasonal peak during the spring, while the males would have the capacity to reproduce throughout the year, given the lack of variation in the testicular weight. This study showed that the population of A. cyclophora from the bonaerensean area is composed mainly of juvenile individuals. The species presents a heterogeneous spatial distribution pattern, concentrating mainly in El Rincón area and off the east and south coast of Uruguay, where the highest abundances were recorded. Atlantoraja cyclophora was captured between 10,9 and 53,6 m depths, at temperatures between 8,5 and 19,2°C, and between 26,6 and 34,1 ppm salinity. For both Río de la Plata and El Rincón areas, the species has a preference for depth and would not be significantly affected by seasonal variations in background temperature. The juveniles are distributed from shallow waters (13 m) to the isobath of 50 m, while adults predominate from 30 m depth to deeper waters. The coastal bonaerensean region is an area that harbors a great variety of marine species and plays an important role in the life cycles of cartilaginous fishes. In turn, this region concentrates the main landing ports for sharks and rays, the latter being declared under the same category without discriminating at a specific level. Atlantoraja cyclophora is caught as an accompanying fauna of other industrial fisheries and is among the main species of rays landed. The zones of greater concentration of the species are composed mainly of ontogenetic stages on which the growth rate of the population depends (juveniles and egg laying females). This fact, added to the prolonged juvenile stage that individuals present, highlights their vulnerability to fishing exploitation. The results of this work provide significant information on the reproductive ecology of A. cyclophora that, in addition to its biological interest, may be useful for the development of management strategies for conservation of the species.

Global trends in commercially valuable teleost fisheries point to substantial deterioration in population size, offering limited potential for increased harvests. Consequently a shift in focus towards alternative fisheries has increased fishing effort towards targeting chondrichthyans as a possible solution to meet global demands. The life-history traits of chondrichthyans make them poor candidates for resolving economic and nutritional security as these make them particularly vulnerable to anthromorphic influences. Current fisheries management approaches based on centralized government intervention have proved inadequate. This failure of current management approaches is often linked with poor co-operation by industry with government when collecting fishery-dependent data. As management decisions are based on quantitative estimates from fishery assessment modes data collected are often of poor quality. Co-management with its implied power-sharing arrangement between government and fishing communities has been proposed as a more realistic alternative. The motivation within industry to collect high quality data can only be created with a feeling of ownership. The decline in linefish species in South Africa has led to increased exploitation of demersal sharks such as Mustelus mustelus. Their status as one of the target and by-catch species of South Africa's shark fisheries necessitated resource assessment. Age, growth, maturity and mortality calculations for M mustelus were made from data collected from 1983-2006. The maximum observed age for M mustelus was 25 years. Estimated von Bertalanffy growth parameters from observed length-at-age for combined sexes, females and males were L∞ = 1946.16 mm TL, K = 0.08 year⁻' , to = -3.63 year⁻'; L∞ = 2202.21mm, K = 0.05 year⁻', to = 4.67 years; and L∞ = 1713.19 mm TL, K = 0.08 year⁻' and to = -4.36 years, respectively. Instantaneous total mortality (Z) was estimated at 0.16 y⁻', whilst natural mortality (M) for M mustelus was estimated at 0.05 y⁻'. The age and length at 50% maturity was determined for combined sexes, females and males at 1216 mm TL corresponding to an age of 9.93 years, 1234 mm (TL) and 10.75 years, and 1106 mm TL and 9.1 years respectively. The smoothhound shark resource off the south-eastern and south-western Cape coast was assessed by three dynamic pool models; yield per recruit, spawner biomass per recruit and an extended yield and spawner biomass per recruit. Due to the longevity of elasmobranches the per-recruit model was extended over a 20 year time-frame to simulate resource responses to management options. Fo.1 was estimated as 0.034 year⁻' and F MAX was estimated as 0.045 year⁻'. FsB50 was estimated as 0.031. The extended per-recruit model tested the outcome of different management scenarios, Size and effort control showed the least probability of pristine biomass falling below 20% of current levels in 20 years (where selectivity was set at 3 years). The replacement yield model showed that the average catches over the past decade are 2.5 times higher than the replacement yield is on the South Coast and 1.30 on the West Coast. A more realistic level optimising yield would be at 0.05 with a selection pattern at 3 years, where the probability of the biomass falling to below 20% of pristine pre-exploited levels in twenty years becomes negligible. A comparison of the models showed that current catches need to be halved for exploitation of smoothhound sharks to be sustainable. The results of this study indicate a need for a management intervention for M mustelus in South Africa with regards to potential overexploitation and collection of quality data for further assessments. A demersal identification key was developed as part of this study, which should aid monitoring officials in accurately identifying shark logs for collecting data. This study showed how adopting a management plan with the inclusion of comanagement concepts would improve the quality of data collected and increase monitoring of fishing activities. The inclusion of co-management is possible due to the unique bottle neck created by few demersal shark processing facilities actively exporting shark. A fishery management plan was compiled proposing several management options including size and effort controls.

Vascular casts of three chondrichthian, one dipnoan, one chondrostean and 14 teleostean species were examined by light and scanning electron microscopy in order to give a qualitative and quantitative analysis of interarterial anastomoses (iaas) that indicate the presence (or absence) of a secondary vascular system (SVS). Anastomoses were found to originate from a variety of different primary blood vessels, many of which have not been previously identified as giving rise to secondary vessels. Segmental arteries derived from the dorsal aorta and supplying body musculature were major sites of origin of the SVS, although there was considerable variation in where, in the hierarchy of arterial branching, the anastomoses occurred. The degree of investment in a SVS was species specific, with more active species having a higher degree of secondary vascularisation. This difference was quantified using an absolute count of iaas between Anguilla reinhardtii and Trachinotus baillonii. A range of general features of the SVS is also described. No evidence of iaas was found on the coeliac, mesenteric or renal circulation in any species. Evidence of interarterial anastomoses were lacking in the dipnoan (Sarcopterygii) and chondrichthyan species examined, suggesting that a SVS is restricted to actinopterygian fishes. The presence and distribution of a secondary vascular system does not appear to be exclusively linked to phylogenetic position, but rather to the physiological adaptation of the species. Histological sections of primary segmental arteries and associated interarterial anastomoses and secondary vessels from the long-finned eel, Anguilla reinhardtii, were examined by light and transmission electron microscopy. Secondary vessels were found to originate from the primary vasculature as depressions through the tunica intima and media, from where they ran perpendicularly to the adventitial layer, before coiling extensively. From here the anastomoses travelled a relatively linear path in the outer margin of the adventitia to re-anastomose with a secondary vessel running in parallel with the primary counterpart. Secondary vessels had a structure quite similar to that of primary vessels; they were lined by endothelial cells on a continuous basement membrane, surrounded by single layer of smooth muscle cells surrounding the vessel. Smooth muscle cells were also found in the vicinity of interarterial anastomoses in the adventitia, but these were more longitudinally orientated. The presence of smooth muscle cells on all aspects of the secondary circulation suggests that this vascular system is regulated in a similar manner as the primary vascular system. Because interarterial anastomoses are structurally integrated with the primary vessel from which they originate, it was anticipated that flow through secondary vessels would to some extent be affected by an increase in primary vascular tone. Immunohistochemical studies showed that primary segmental arteries displayed moderate immunoreactivity to antibodies against 5-hydroxytryptamine and substance P, while interarterial anastomoses and secondary vessels showed dense immunoreactivity. Secondary vessels were followed to the surface of the animal through consecutive sections, where they eventually give rise to capillary beds overlying the scales. Secondary capillary beds were found to supply chloride cells in the skin, suggesting that this vascular system may be involved in cutaneous ionic exchange. Branchial vascular casts from two species of Tetraodontiformes showed that the vessels previously reported as nutrient vessels are with certainty part of the secondary vascular system. In the three-barred porcupine fish, Dicotylichthys punctulatus, interarterial anastomoses originated at high densities from efferent filamental and the efferent branchial arteries, from where they formed progressively larger secondary vessels. Small branches of this vascular system entered the filament body, where it gave rise to numerous side-vessels along the way. Large secondary vessels running in parallel with the efferent branchial arteries were found to constitute an additional arterio-arterial pathway, in that they exited the branchial basket in company with the afferent mandibular artery, the carotid artery and the efferent branchial arteries, from where they gave rise to vascular beds immediately after exit. The secondary vessels in this species were not found to supply the filament musculature; rather this vascular system was supplied by a single vessel derived from the efferent branchial artery, running in parallel with the afferent branchial artery. Secondary vessels were not found on any branchial component in the banded toadfish, Marylina pleurosticta, but in all other aspects the branchial vascular anatomy was similar to that of D. punctulatus. It is proposed that four independent vascular pathways may be present in the teleostean gill. The blood volume and flow rates of the primary (PVS) and secondary vascular system (SVS) were examined in the catadromous euryhaline teleost Lates calcarifer in order to determine whether any of these parameters were subject to change in individuals acclimated to seawater, compared to a group acclimated to freshwater. There was no significant difference in any measured parameter for the two groups. The volumes of the SVS were 0.67 „b 0.13 and 0.76 „b 0.13 mL 100g-1 body mass for FW and SW acclimated animals respectively. This constituted approximately one-third of the total blood volume in both groups. Turnover times for the SVS ranged from 21.0 to 25.2 minutes, demonstrating in accordance with previous publications, that this system is considerably more dynamic than previously assumed.

Vascular casts of three chondrichthian, one dipnoan, one chondrostean and 14 teleostean species were examined by light and scanning electron microscopy in order to give a qualitative and quantitative analysis of interarterial anastomoses (iaas) that indicate the presence (or absence) of a secondary vascular system (SVS). Anastomoses were found to originate from a variety of different primary blood vessels, many of which have not been previously identified as giving rise to secondary vessels. Segmental arteries derived from the dorsal aorta and supplying body musculature were major sites of origin of the SVS, although there was considerable variation in where, in the hierarchy of arterial branching, the anastomoses occurred. The degree of investment in a SVS was species specific, with more active species having a higher degree of secondary vascularisation. This difference was quantified using an absolute count of iaas between Anguilla reinhardtii and Trachinotus baillonii. A range of general features of the SVS is also described. No evidence of iaas was found on the coeliac, mesenteric or renal circulation in any species. Evidence of interarterial anastomoses were lacking in the dipnoan (Sarcopterygii) and chondrichthyan species examined, suggesting that a SVS is restricted to actinopterygian fishes. The presence and distribution of a secondary vascular system does not appear to be exclusively linked to phylogenetic position, but rather to the physiological adaptation of the species. Histological sections of primary segmental arteries and associated interarterial anastomoses and secondary vessels from the long-finned eel, Anguilla reinhardtii, were examined by light and transmission electron microscopy. Secondary vessels were found to originate from the primary vasculature as depressions through the tunica intima and media, from where they ran perpendicularly to the adventitial layer, before coiling extensively. From here the anastomoses travelled a relatively linear path in the outer margin of the adventitia to re-anastomose with a secondary vessel running in parallel with the primary counterpart. Secondary vessels had a structure quite similar to that of primary vessels; they were lined by endothelial cells on a continuous basement membrane, surrounded by single layer of smooth muscle cells surrounding the vessel. Smooth muscle cells were also found in the vicinity of interarterial anastomoses in the adventitia, but these were more longitudinally orientated. The presence of smooth muscle cells on all aspects of the secondary circulation suggests that this vascular system is regulated in a similar manner as the primary vascular system. Because interarterial anastomoses are structurally integrated with the primary vessel from which they originate, it was anticipated that flow through secondary vessels would to some extent be affected by an increase in primary vascular tone. Immunohistochemical studies showed that primary segmental arteries displayed moderate immunoreactivity to antibodies against 5-hydroxytryptamine and substance P, while interarterial anastomoses and secondary vessels showed dense immunoreactivity. Secondary vessels were followed to the surface of the animal through consecutive sections, where they eventually give rise to capillary beds overlying the scales. Secondary capillary beds were found to supply chloride cells in the skin, suggesting that this vascular system may be involved in cutaneous ionic exchange. Branchial vascular casts from two species of Tetraodontiformes showed that the vessels previously reported as nutrient vessels are with certainty part of the secondary vascular system. In the three-barred porcupine fish, Dicotylichthys punctulatus, interarterial anastomoses originated at high densities from efferent filamental and the efferent branchial arteries, from where they formed progressively larger secondary vessels. Small branches of this vascular system entered the filament body, where it gave rise to numerous side-vessels along the way. Large secondary vessels running in parallel with the efferent branchial arteries were found to constitute an additional arterio-arterial pathway, in that they exited the branchial basket in company with the afferent mandibular artery, the carotid artery and the efferent branchial arteries, from where they gave rise to vascular beds immediately after exit. The secondary vessels in this species were not found to supply the filament musculature; rather this vascular system was supplied by a single vessel derived from the efferent branchial artery, running in parallel with the afferent branchial artery. Secondary vessels were not found on any branchial component in the banded toadfish, Marylina pleurosticta, but in all other aspects the branchial vascular anatomy was similar to that of D. punctulatus. It is proposed that four independent vascular pathways may be present in the teleostean gill. The blood volume and flow rates of the primary (PVS) and secondary vascular system (SVS) were examined in the catadromous euryhaline teleost Lates calcarifer in order to determine whether any of these parameters were subject to change in individuals acclimated to seawater, compared to a group acclimated to freshwater. There was no significant difference in any measured parameter for the two groups. The volumes of the SVS were 0.67 „b 0.13 and 0.76 „b 0.13 mL 100g-1 body mass for FW and SW acclimated animals respectively. This constituted approximately one-third of the total blood volume in both groups. Turnover times for the SVS ranged from 21.0 to 25.2 minutes, demonstrating in accordance with previous publications, that this system is considerably more dynamic than previously assumed.

Vascular casts of three chondrichthian, one dipnoan, one chondrostean and 14 teleostean species were examined by light and scanning electron microscopy in order to give a qualitative and quantitative analysis of interarterial anastomoses (iaas) that indicate the presence (or absence) of a secondary vascular system (SVS). Anastomoses were found to originate from a variety of different primary blood vessels, many of which have not been previously identified as giving rise to secondary vessels. Segmental arteries derived from the dorsal aorta and supplying body musculature were major sites of origin of the SVS, although there was considerable variation in where, in the hierarchy of arterial branching, the anastomoses occurred. The degree of investment in a SVS was species specific, with more active species having a higher degree of secondary vascularisation. This difference was quantified using an absolute count of iaas between Anguilla reinhardtii and Trachinotus baillonii. A range of general features of the SVS is also described. No evidence of iaas was found on the coeliac, mesenteric or renal circulation in any species. Evidence of interarterial anastomoses were lacking in the dipnoan (Sarcopterygii) and chondrichthyan species examined, suggesting that a SVS is restricted to actinopterygian fishes. The presence and distribution of a secondary vascular system does not appear to be exclusively linked to phylogenetic position, but rather to the physiological adaptation of the species. Histological sections of primary segmental arteries and associated interarterial anastomoses and secondary vessels from the long-finned eel, Anguilla reinhardtii, were examined by light and transmission electron microscopy. Secondary vessels were found to originate from the primary vasculature as depressions through the tunica intima and media, from where they ran perpendicularly to the adventitial layer, before coiling extensively. From here the anastomoses travelled a relatively linear path in the outer margin of the adventitia to re-anastomose with a secondary vessel running in parallel with the primary counterpart. Secondary vessels had a structure quite similar to that of primary vessels; they were lined by endothelial cells on a continuous basement membrane, surrounded by single layer of smooth muscle cells surrounding the vessel. Smooth muscle cells were also found in the vicinity of interarterial anastomoses in the adventitia, but these were more longitudinally orientated. The presence of smooth muscle cells on all aspects of the secondary circulation suggests that this vascular system is regulated in a similar manner as the primary vascular system. Because interarterial anastomoses are structurally integrated with the primary vessel from which they originate, it was anticipated that flow through secondary vessels would to some extent be affected by an increase in primary vascular tone. Immunohistochemical studies showed that primary segmental arteries displayed moderate immunoreactivity to antibodies against 5-hydroxytryptamine and substance P, while interarterial anastomoses and secondary vessels showed dense immunoreactivity. Secondary vessels were followed to the surface of the animal through consecutive sections, where they eventually give rise to capillary beds overlying the scales. Secondary capillary beds were found to supply chloride cells in the skin, suggesting that this vascular system may be involved in cutaneous ionic exchange. Branchial vascular casts from two species of Tetraodontiformes showed that the vessels previously reported as nutrient vessels are with certainty part of the secondary vascular system. In the three-barred porcupine fish, Dicotylichthys punctulatus, interarterial anastomoses originated at high densities from efferent filamental and the efferent branchial arteries, from where they formed progressively larger secondary vessels. Small branches of this vascular system entered the filament body, where it gave rise to numerous side-vessels along the way. Large secondary vessels running in parallel with the efferent branchial arteries were found to constitute an additional arterio-arterial pathway, in that they exited the branchial basket in company with the afferent mandibular artery, the carotid artery and the efferent branchial arteries, from where they gave rise to vascular beds immediately after exit. The secondary vessels in this species were not found to supply the filament musculature; rather this vascular system was supplied by a single vessel derived from the efferent branchial artery, running in parallel with the afferent branchial artery. Secondary vessels were not found on any branchial component in the banded toadfish, Marylina pleurosticta, but in all other aspects the branchial vascular anatomy was similar to that of D. punctulatus. It is proposed that four independent vascular pathways may be present in the teleostean gill. The blood volume and flow rates of the primary (PVS) and secondary vascular system (SVS) were examined in the catadromous euryhaline teleost Lates calcarifer in order to determine whether any of these parameters were subject to change in individuals acclimated to seawater, compared to a group acclimated to freshwater. There was no significant difference in any measured parameter for the two groups. The volumes of the SVS were 0.67 „b 0.13 and 0.76 „b 0.13 mL 100g-1 body mass for FW and SW acclimated animals respectively. This constituted approximately one-third of the total blood volume in both groups. Turnover times for the SVS ranged from 21.0 to 25.2 minutes, demonstrating in accordance with previous publications, that this system is considerably more dynamic than previously assumed.

Vascular casts of three chondrichthian, one dipnoan, one chondrostean and 14 teleostean species were examined by light and scanning electron microscopy in order to give a qualitative and quantitative analysis of interarterial anastomoses (iaas) that indicate the presence (or absence) of a secondary vascular system (SVS). Anastomoses were found to originate from a variety of different primary blood vessels, many of which have not been previously identified as giving rise to secondary vessels. Segmental arteries derived from the dorsal aorta and supplying body musculature were major sites of origin of the SVS, although there was considerable variation in where, in the hierarchy of arterial branching, the anastomoses occurred. The degree of investment in a SVS was species specific, with more active species having a higher degree of secondary vascularisation. This difference was quantified using an absolute count of iaas between Anguilla reinhardtii and Trachinotus baillonii. A range of general features of the SVS is also described. No evidence of iaas was found on the coeliac, mesenteric or renal circulation in any species. Evidence of interarterial anastomoses were lacking in the dipnoan (Sarcopterygii) and chondrichthyan species examined, suggesting that a SVS is restricted to actinopterygian fishes. The presence and distribution of a secondary vascular system does not appear to be exclusively linked to phylogenetic position, but rather to the physiological adaptation of the species. Histological sections of primary segmental arteries and associated interarterial anastomoses and secondary vessels from the long-finned eel, Anguilla reinhardtii, were examined by light and transmission electron microscopy. Secondary vessels were found to originate from the primary vasculature as depressions through the tunica intima and media, from where they ran perpendicularly to the adventitial layer, before coiling extensively. From here the anastomoses travelled a relatively linear path in the outer margin of the adventitia to re-anastomose with a secondary vessel running in parallel with the primary counterpart. Secondary vessels had a structure quite similar to that of primary vessels; they were lined by endothelial cells on a continuous basement membrane, surrounded by single layer of smooth muscle cells surrounding the vessel. Smooth muscle cells were also found in the vicinity of interarterial anastomoses in the adventitia, but these were more longitudinally orientated. The presence of smooth muscle cells on all aspects of the secondary circulation suggests that this vascular system is regulated in a similar manner as the primary vascular system. Because interarterial anastomoses are structurally integrated with the primary vessel from which they originate, it was anticipated that flow through secondary vessels would to some extent be affected by an increase in primary vascular tone. Immunohistochemical studies showed that primary segmental arteries displayed moderate immunoreactivity to antibodies against 5-hydroxytryptamine and substance P, while interarterial anastomoses and secondary vessels showed dense immunoreactivity. Secondary vessels were followed to the surface of the animal through consecutive sections, where they eventually give rise to capillary beds overlying the scales. Secondary capillary beds were found to supply chloride cells in the skin, suggesting that this vascular system may be involved in cutaneous ionic exchange. Branchial vascular casts from two species of Tetraodontiformes showed that the vessels previously reported as nutrient vessels are with certainty part of the secondary vascular system. In the three-barred porcupine fish, Dicotylichthys punctulatus, interarterial anastomoses originated at high densities from efferent filamental and the efferent branchial arteries, from where they formed progressively larger secondary vessels. Small branches of this vascular system entered the filament body, where it gave rise to numerous side-vessels along the way. Large secondary vessels running in parallel with the efferent branchial arteries were found to constitute an additional arterio-arterial pathway, in that they exited the branchial basket in company with the afferent mandibular artery, the carotid artery and the efferent branchial arteries, from where they gave rise to vascular beds immediately after exit. The secondary vessels in this species were not found to supply the filament musculature; rather this vascular system was supplied by a single vessel derived from the efferent branchial artery, running in parallel with the afferent branchial artery. Secondary vessels were not found on any branchial component in the banded toadfish, Marylina pleurosticta, but in all other aspects the branchial vascular anatomy was similar to that of D. punctulatus. It is proposed that four independent vascular pathways may be present in the teleostean gill. The blood volume and flow rates of the primary (PVS) and secondary vascular system (SVS) were examined in the catadromous euryhaline teleost Lates calcarifer in order to determine whether any of these parameters were subject to change in individuals acclimated to seawater, compared to a group acclimated to freshwater. There was no significant difference in any measured parameter for the two groups. The volumes of the SVS were 0.67 „b 0.13 and 0.76 „b 0.13 mL 100g-1 body mass for FW and SW acclimated animals respectively. This constituted approximately one-third of the total blood volume in both groups. Turnover times for the SVS ranged from 21.0 to 25.2 minutes, demonstrating in accordance with previous publications, that this system is considerably more dynamic than previously assumed.